Galaxy And Mass Assembly (GAMA): mass-size relations of z < 0.1 galaxies subdivided by Sérsic index, colour and morphology

We use data from the Galaxy And Mass Assembly (GAMA) survey in the redshift range 0.01 < z < 0.1 (8399 galaxies in g to K_s bands) to derive the stellar mass–half-light radius relations for various divisions of ‘early’- and ‘late’-type samples. We find that the choice of division between early and late (i.e. colour, shape, morphology) is not particularly critical; however, the adopted mass limits and sample selections (i.e. the careful rejection of outliers and use of robust fitting methods) are important. In particular, we note that for samples extending to low stellar mass limits <10¹⁰Μ_Θ the Sérsic index bimodality, evident for high-mass systems, becomes less distinct and no-longer acts as a reliable separator of early- and late-type systems. The final set of stellar mass–half-light radius relations are reported for a variety of galaxy population subsets in 10 bands (ugrizZY JHK_s) and are intended to provide a comprehensive low-z benchmark for the many ongoing high-z studies. Exploring the variation of the stellar mass–half-light radius relations with wavelength, we confirm earlier findings that galaxies appear more compact at longer wavelengths albeit at a smaller level than previously noted: at <10¹⁰Μ_Θ both spiral systems and ellipticals show a decrease in size of 13 per cent from g to K_s (which is near linear in log wavelength). Finally, we note that the sizes used in this work are derived from 2D Sérsic light profile fitting (using GALFIT3), i.e. elliptical semimajor half-light radii, improving on earlier low-z benchmarks based on circular apertures.